Field of the Invention
The present invention relates to a coating, a cutting tool, and a method of manufacturing a coating, and particularly to a coating excellent in resistance to oxidation and hardness, a cutting tool including the coating, and a method of manufacturing the coating.
Description of the Background Art
Steel or a casting has conventionally been cut with a cutting tool composed of cemented carbide. Since a cutting edge of such a cutting tool is exposed to a severe environment such as a high temperature or a high pressure during cutting, wear or chipping of the cutting edge tends to occur. Thus, cutting performance of a cutting tool presents a challenge.
In order to improve cutting performance of a cutting tool, a coating for a surface of a substrate composed of cemented carbide or the like has been developed. Among others, a coating composed of a nitride containing titanium and aluminum (hereinafter also referred to as “Ti1-xAlxN”) can have high hardness and enhanced resistance to oxidation resulting from increase in content x of Al. By coating a cutting tool with such a coating, performance of the cutting tool can noticeably be improved and further development of the coating is expected.
For example, Japanese Patent Laying-Open No. 7-205362 discloses a coating having a multi-layer structure in which composition is continuously varied with a period of a TiN layer and an AlN layer from 0.4 nm to 50 nm. Ti1-xAlxN seems to be present in the period of the multi-layer structure. This coating, however, is formed with physical vapor deposition (PVD), and hence x in Ti1-xAlxN could not be designed to be higher than 0.55. Therefore, resistance to oxidation of this coating has been limited and further improvement has been demanded.
Japanese National Patent Publication No. 2008-545063 discloses a technique for fabricating a coating composed of Ti1-xAlxN with chemical vapor deposition (CVD). Japanese National Patent Publication No. 2008-545063 discloses a coating having a face-centered cubic structure (hereinafter also referred to as an “fcc crystal structure”) in which x in Ti1-xAlxN satisfies a condition of 0.75<x≤0.93.